Due to mounting concerns over air quality, numerous jurisdictions in North America, Europe and Asia have instituted mandatory testing programs wherein exhaust emissions of vehicles are tested to determine whether they meet minimum standards set by a government agency. Typically, this testing of exhaust emissions is conducted annually and is a necessary precondition to renewal of vehicle registration. United States government standards for volatile organic compounds, oxides of nitrogen and carbon monoxide as defined by the U.S. Environmental Protection Agency are contained in the Federal Register, Part 51.
It has been found that most vehicles meet emissions standards. Most vehicle-related air pollution is caused by a relatively small proportion of vehicles, many of which have emission control systems which are malfunctioning or have been tampered with.
Presently used tests to accurately determine emission levels and to diagnose problems with vehicle emission controls are time consuming. Typically, vehicles must be brought to a central testing facility, and tested on a stationary testing apparatus by direct sampling of the exhaust.
The disadvantage exists that widespread testing of vehicles using stationary testing apparatus is very time consuming. This results in undue hardship for motorists, who must endure long lineups at testing facilities.
Another disadvantage exists that stationary testing apparatus is very expensive, and therefore the cost of testing a vehicle on stationary apparatus is relatively high.
There are also presently available remote sensing testing apparatus which quickly test exhaust emissions by spectroscopic methods, which may generally be defined as methods which detect the presence of a substance by measurement of the radiant energy absorbed or emitted by the substance in any of the wavelengths of the electromagnetic spectrum. For example, presently available remote sensing testing apparatus typically test exhaust emissions by the use of ultrasensitive infrared detection technology. Remote sensing testing apparatus utilizing ultrasensitive infrared detection technology typically operates by passing a chopped infrared beam through the exhaust plume of a vehicle in close proximity to the exhaust pipe of the vehicle. The absorption intensity of the beam is measured after it is passed through the exhaust plume and the levels of certain target compounds present in the exhaust emissions of the vehicle are then calculated.
In conclusion, the disadvantage exists that accurate testing of vehicle emissions using stationary testing apparatus is time consuming and expensive. Although quicker and cheaper, remote sensing testing is typically less accurate than stationary testing in estimating levels of vehicle emissions.